The present invention relates broadly to flexible plastic, i.e., polymeric, tubing constructions, and more particularly to a multi-layer or other composite tubing construction which is provided as having, for example, one or more longitudinal bands of a generally transparent material formed into an otherwise generally opaque sidewall of the tubing so as to provide for a sight glass window through which the contents of the tubing may be viewed.
Flexible plastic tubing of the type herein involved is used in a variety of fluid transfer applications as shown in U.S. Pat. Nos. 3,070,132; 3,561,493; 3,605,750; 3,752,617; 3,825,036; 3,907,955; 4,276,250; 4,330,497; 4,662,404; 4,888,146; 5,258,160; 5,456,674; 5,533,985; 6,036,682; in European Pat. Nos. 385,730; 385,732; 829,340; and in Japanese Patent Nos. 304225 and 304226. In certain applications, it is necessary to view inside the tubing for monitoring or inspection purposes, or otherwise for confirming the contents of the tubing. For these applications, it therefore is required that the tubing sidewall be generally transparent.
In these same applications, however, it also may be required that the tubing exhibits additional capabilities such as flame retardancy or other environmental resistance. Generally, these additional capabilities are achieved via the introduction of additives which are loaded at a result effective level into the base polymer system. As a result of such loading, a normally clear or transparent polymer, such as an acrylic, nylon, polyvinyl chloride (PVC), polyolefin, polyethylene terephthalate (PET), thermoplastic rubber (TPR), polybutylene terephthalate (PBT), ethylene vinyl acetate (EVA), polycarbonate, polyvinylidene fluoride (PVDF), polyamide, polymethylmethacrylate (PMMA), or liquid crystal polymer (LCP) may be rendered opaque.
One such application which has been identified by the present inventors as requiring both transparency and fire resistance involves the use of tubing in the installation of telecommunication and other networks. In what are known as xe2x80x9cair blown fiberxe2x80x9d (ABF) installations, a compressed gas such as dry air or nitrogen is used xe2x80x9cblowxe2x80x9d small, lightweight multi-fiber optical cables into flexible plastic tubing or multi-tube bundles thereof which have been previously installed along the network routing. The optical cable itself typically comprises a plastic outer sheath surrounding one or more optical fibers. The cable is advanced along the routing of the tubes by the fluid drag of the gas flowing in the tubing. ABF installations are further described in U.S. Pat. Nos. 6,024,387; 5,781,678; 5,664,763; 5,499,797; 5,065,928; 5,022,634; 4,990,033; 4,850,569; 4,796,970; 4,691,896; and in Japanese Pat. Nos. 8331725 and 6201923. Commercial ABF systems are marketed under the name FutureFlex(copyright) by Sumitomo Electric Lightwave Corp., Research Triangle Park, NC.
Conventional tubing used in ABF applications is believed not to be transparent, however, as would afford an ability to view the optical cables within the tubing to facilitate installation, servicing, or administration. In this regard, building codes and other regulations typically specify at least some degree or fire resistance for the tubing which heretofore has necessitated the use of opaque materials of construction.
As has been seen, circumstances sometimes dictate that the flexible plastic tubing herein involved must meet seemingly incompatible requirements such as transparency and flame resistance. Accordingly, it is believed that tubing constructions offering a capability for the provision of such features would be well-received, for example, by the ABF market.
The present invention is directed to flexible plastic, i.e., polymeric, tubing constructions, and particularly to a multi-layer or other composite construction which is provided as having, for example, one or more longitudinal bands of a generally transparent material formed into an otherwise generally opaque sidewall of the tubing so as to provide for a sight glass window capability through which the contents of the tubing may be viewed. Accordingly, the tubing construction of the invention herein involved is particularly adapted for use in ABF applications and other cable or wire installations wherein the ability to view the cables or wires within the tubing is desired for installation, servicing, or administration.
Advantageously, in allowing for a major portion of the tubing sidewall to be opaque with a minor portion thereof being transparent, the tubing construction of the present invention is able to provide a sight glass capability without compromising flame resistance or other chemical or physical properties. In this regard, the majority of the tubing may be formed of a base polymer which is loaded with one or more opacifying fillers to be rendered fire resistant or otherwise to exhibit other enhanced chemical or physical properties, with the remainder of the tubing being formed of the unfilled base polymer which remains transparent. From known theory, it may be predicted that the addition of less than a critical amount of unfilled polymer to the filled system would not appreciably affect the fire resistance of the system.
In accordance with the precepts of the present invention, the tubing is formed as having a first sidewall segment formed of a first polymeric material which is generally opaque, and a second sidewall segment which is co-extruded or otherwise formed integrally with the first sidewall segment of a second polymeric material which is generally transparent. The second sidewall segment has an axial inner surface which defines at least a portion of the innermost surface of the tubing, and an axial outer surface which defines a portion of the outermost surface of the tubing. The inner and outer surfaces further define a window therebetween through the thickness dimension of the tubing sidewall, with the contents of the tubing being viewable through the window.
In an illustrative embodiment, the second sidewall segment is formed as first and second longitudinal bands with the first sidewall segment extending radially therebetween. Each of the bands may be provided to extend substantially continuously along the length of the tubing, with the first longitudinal band being disposed at a first radial position relative to the circumferential extent of the tubing. The second longitudinal band, in turn, may be disposed at a second radial position opposite the first radial position so as to allow for the backlighting of the tubing during inspection.
In another illustrative embodiment, the tubing includes a third sidewall segment formed integrally with the first and second segments as having inner surface which defines a portion of tubing innermost surface. Such inner surface may be profiled as defining a series of radially-disposed longitudinal splines, ribs, or other projections. With respect to ABF installations, such projections have been observed to reduce surface area contact between the cable and tubing sidewall which results in correspondingly decreased friction as the cable is blown through the tubing. Such projections also develop a lower velocity boundary layer in the gas flow near the sidewall surface which has the tendency to direct the fiber into the higher velocity flow towards the center of the tubing. The end result is less drag on the tubing which facilitates long runs and directional changes such as around bends.
The present invention, accordingly, comprises the construction, combination of elements, and arrangement of parts of which are exemplified in the detailed disclosure to follow. Advantages of the present invention include a flexible plastic tubing construction which is provided as having a sight-glass capability without affecting the gross fire resistance, electrical conductivity, or other specified chemical or physical properties of the tubing. Additional advantages include a tubing construction which is economical to manufacture in long, continuous lengths, and which further is particularly adapted for use in ABF installations. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.